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32 results

p2m.c

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  • open.c 24.60 KiB
    /*
     *  linux/fs/open.c
     *
     *  Copyright (C) 1991, 1992  Linus Torvalds
     */
    
    #include <linux/string.h>
    #include <linux/mm.h>
    #include <linux/file.h>
    #include <linux/fdtable.h>
    #include <linux/fsnotify.h>
    #include <linux/module.h>
    #include <linux/tty.h>
    #include <linux/namei.h>
    #include <linux/backing-dev.h>
    #include <linux/capability.h>
    #include <linux/securebits.h>
    #include <linux/security.h>
    #include <linux/mount.h>
    #include <linux/fcntl.h>
    #include <linux/slab.h>
    #include <asm/uaccess.h>
    #include <linux/fs.h>
    #include <linux/personality.h>
    #include <linux/pagemap.h>
    #include <linux/syscalls.h>
    #include <linux/rcupdate.h>
    #include <linux/audit.h>
    #include <linux/falloc.h>
    #include <linux/fs_struct.h>
    #include <linux/ima.h>
    #include <linux/dnotify.h>
    #include <linux/compat.h>
    
    #include "internal.h"
    
    int do_truncate(struct dentry *dentry, loff_t length, unsigned int time_attrs,
    	struct file *filp)
    {
    	int ret;
    	struct iattr newattrs;
    
    	/* Not pretty: "inode->i_size" shouldn't really be signed. But it is. */
    	if (length < 0)
    		return -EINVAL;
    
    	newattrs.ia_size = length;
    	newattrs.ia_valid = ATTR_SIZE | time_attrs;
    	if (filp) {
    		newattrs.ia_file = filp;
    		newattrs.ia_valid |= ATTR_FILE;
    	}
    
    	/* Remove suid/sgid on truncate too */
    	ret = should_remove_suid(dentry);
    	if (ret)
    		newattrs.ia_valid |= ret | ATTR_FORCE;
    
    	mutex_lock(&dentry->d_inode->i_mutex);
    	ret = notify_change(dentry, &newattrs);
    	mutex_unlock(&dentry->d_inode->i_mutex);
    	return ret;
    }
    
    long vfs_truncate(struct path *path, loff_t length)
    {
    	struct inode *inode;
    	long error;
    
    	inode = path->dentry->d_inode;
    
    	/* For directories it's -EISDIR, for other non-regulars - -EINVAL */
    	if (S_ISDIR(inode->i_mode))
    		return -EISDIR;
    	if (!S_ISREG(inode->i_mode))
    		return -EINVAL;
    
    	error = mnt_want_write(path->mnt);
    	if (error)
    		goto out;
    
    	error = inode_permission(inode, MAY_WRITE);
    	if (error)
    		goto mnt_drop_write_and_out;
    
    	error = -EPERM;
    	if (IS_APPEND(inode))
    		goto mnt_drop_write_and_out;
    
    	error = get_write_access(inode);
    	if (error)
    		goto mnt_drop_write_and_out;
    
    	/*
    	 * Make sure that there are no leases.  get_write_access() protects
    	 * against the truncate racing with a lease-granting setlease().
    	 */
    	error = break_lease(inode, O_WRONLY);
    	if (error)
    		goto put_write_and_out;
    
    	error = locks_verify_truncate(inode, NULL, length);
    	if (!error)
    		error = security_path_truncate(path);
    	if (!error)
    		error = do_truncate(path->dentry, length, 0, NULL);
    
    put_write_and_out:
    	put_write_access(inode);
    mnt_drop_write_and_out:
    	mnt_drop_write(path->mnt);
    out:
    	return error;
    }
    EXPORT_SYMBOL_GPL(vfs_truncate);
    
    static long do_sys_truncate(const char __user *pathname, loff_t length)
    {
    	unsigned int lookup_flags = LOOKUP_FOLLOW;
    	struct path path;
    	int error;
    
    	if (length < 0)	/* sorry, but loff_t says... */
    		return -EINVAL;
    
    retry:
    	error = user_path_at(AT_FDCWD, pathname, lookup_flags, &path);
    	if (!error) {
    		error = vfs_truncate(&path, length);
    		path_put(&path);
    	}
    	if (retry_estale(error, lookup_flags)) {
    		lookup_flags |= LOOKUP_REVAL;
    		goto retry;
    	}
    	return error;
    }
    
    SYSCALL_DEFINE2(truncate, const char __user *, path, long, length)
    {
    	return do_sys_truncate(path, length);
    }
    
    #ifdef CONFIG_COMPAT
    COMPAT_SYSCALL_DEFINE2(truncate, const char __user *, path, compat_off_t, length)
    {
    	return do_sys_truncate(path, length);
    }
    #endif
    
    static long do_sys_ftruncate(unsigned int fd, loff_t length, int small)
    {
    	struct inode *inode;
    	struct dentry *dentry;
    	struct fd f;
    	int error;
    
    	error = -EINVAL;
    	if (length < 0)
    		goto out;
    	error = -EBADF;
    	f = fdget(fd);
    	if (!f.file)
    		goto out;
    
    	/* explicitly opened as large or we are on 64-bit box */
    	if (f.file->f_flags & O_LARGEFILE)
    		small = 0;
    
    	dentry = f.file->f_path.dentry;
    	inode = dentry->d_inode;
    	error = -EINVAL;
    	if (!S_ISREG(inode->i_mode) || !(f.file->f_mode & FMODE_WRITE))
    		goto out_putf;
    
    	error = -EINVAL;
    	/* Cannot ftruncate over 2^31 bytes without large file support */
    	if (small && length > MAX_NON_LFS)
    		goto out_putf;
    
    	error = -EPERM;
    	if (IS_APPEND(inode))
    		goto out_putf;
    
    	sb_start_write(inode->i_sb);
    	error = locks_verify_truncate(inode, f.file, length);
    	if (!error)
    		error = security_path_truncate(&f.file->f_path);
    	if (!error)
    		error = do_truncate(dentry, length, ATTR_MTIME|ATTR_CTIME, f.file);
    	sb_end_write(inode->i_sb);
    out_putf:
    	fdput(f);
    out:
    	return error;
    }
    
    SYSCALL_DEFINE2(ftruncate, unsigned int, fd, unsigned long, length)
    {
    	return do_sys_ftruncate(fd, length, 1);
    }
    
    #ifdef CONFIG_COMPAT
    COMPAT_SYSCALL_DEFINE2(ftruncate, unsigned int, fd, compat_ulong_t, length)
    {
    	return do_sys_ftruncate(fd, length, 1);
    }
    #endif
    
    /* LFS versions of truncate are only needed on 32 bit machines */
    #if BITS_PER_LONG == 32
    SYSCALL_DEFINE2(truncate64, const char __user *, path, loff_t, length)
    {
    	return do_sys_truncate(path, length);
    }
    
    SYSCALL_DEFINE2(ftruncate64, unsigned int, fd, loff_t, length)
    {
    	return do_sys_ftruncate(fd, length, 0);
    }
    #endif /* BITS_PER_LONG == 32 */
    
    
    int do_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
    {
    	struct inode *inode = file_inode(file);
    	long ret;
    
    	if (offset < 0 || len <= 0)
    		return -EINVAL;
    
    	/* Return error if mode is not supported */
    	if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE))
    		return -EOPNOTSUPP;
    
    	/* Punch hole must have keep size set */
    	if ((mode & FALLOC_FL_PUNCH_HOLE) &&
    	    !(mode & FALLOC_FL_KEEP_SIZE))
    		return -EOPNOTSUPP;
    
    	if (!(file->f_mode & FMODE_WRITE))
    		return -EBADF;
    
    	/* It's not possible punch hole on append only file */
    	if (mode & FALLOC_FL_PUNCH_HOLE && IS_APPEND(inode))
    		return -EPERM;
    
    	if (IS_IMMUTABLE(inode))
    		return -EPERM;
    
    	/*
    	 * Revalidate the write permissions, in case security policy has
    	 * changed since the files were opened.
    	 */
    	ret = security_file_permission(file, MAY_WRITE);
    	if (ret)
    		return ret;
    
    	if (S_ISFIFO(inode->i_mode))
    		return -ESPIPE;
    
    	/*
    	 * Let individual file system decide if it supports preallocation
    	 * for directories or not.
    	 */
    	if (!S_ISREG(inode->i_mode) && !S_ISDIR(inode->i_mode))
    		return -ENODEV;
    
    	/* Check for wrap through zero too */
    	if (((offset + len) > inode->i_sb->s_maxbytes) || ((offset + len) < 0))
    		return -EFBIG;
    
    	if (!file->f_op->fallocate)
    		return -EOPNOTSUPP;
    
    	sb_start_write(inode->i_sb);
    	ret = file->f_op->fallocate(file, mode, offset, len);
    	sb_end_write(inode->i_sb);
    	return ret;
    }
    
    SYSCALL_DEFINE4(fallocate, int, fd, int, mode, loff_t, offset, loff_t, len)
    {
    	struct fd f = fdget(fd);
    	int error = -EBADF;
    
    	if (f.file) {
    		error = do_fallocate(f.file, mode, offset, len);
    		fdput(f);
    	}
    	return error;
    }
    
    /*
     * access() needs to use the real uid/gid, not the effective uid/gid.
     * We do this by temporarily clearing all FS-related capabilities and
     * switching the fsuid/fsgid around to the real ones.
     */
    SYSCALL_DEFINE3(faccessat, int, dfd, const char __user *, filename, int, mode)
    {
    	const struct cred *old_cred;
    	struct cred *override_cred;
    	struct path path;
    	struct inode *inode;
    	int res;
    	unsigned int lookup_flags = LOOKUP_FOLLOW;
    
    	if (mode & ~S_IRWXO)	/* where's F_OK, X_OK, W_OK, R_OK? */
    		return -EINVAL;
    
    	override_cred = prepare_creds();
    	if (!override_cred)
    		return -ENOMEM;
    
    	override_cred->fsuid = override_cred->uid;
    	override_cred->fsgid = override_cred->gid;
    
    	if (!issecure(SECURE_NO_SETUID_FIXUP)) {
    		/* Clear the capabilities if we switch to a non-root user */
    		kuid_t root_uid = make_kuid(override_cred->user_ns, 0);
    		if (!uid_eq(override_cred->uid, root_uid))
    			cap_clear(override_cred->cap_effective);
    		else
    			override_cred->cap_effective =
    				override_cred->cap_permitted;
    	}
    
    	old_cred = override_creds(override_cred);
    retry:
    	res = user_path_at(dfd, filename, lookup_flags, &path);
    	if (res)
    		goto out;
    
    	inode = path.dentry->d_inode;
    
    	if ((mode & MAY_EXEC) && S_ISREG(inode->i_mode)) {
    		/*
    		 * MAY_EXEC on regular files is denied if the fs is mounted
    		 * with the "noexec" flag.
    		 */
    		res = -EACCES;
    		if (path.mnt->mnt_flags & MNT_NOEXEC)
    			goto out_path_release;
    	}
    
    	res = inode_permission(inode, mode | MAY_ACCESS);
    	/* SuS v2 requires we report a read only fs too */
    	if (res || !(mode & S_IWOTH) || special_file(inode->i_mode))
    		goto out_path_release;
    	/*
    	 * This is a rare case where using __mnt_is_readonly()
    	 * is OK without a mnt_want/drop_write() pair.  Since
    	 * no actual write to the fs is performed here, we do
    	 * not need to telegraph to that to anyone.
    	 *
    	 * By doing this, we accept that this access is
    	 * inherently racy and know that the fs may change
    	 * state before we even see this result.
    	 */
    	if (__mnt_is_readonly(path.mnt))
    		res = -EROFS;
    
    out_path_release:
    	path_put(&path);
    	if (retry_estale(res, lookup_flags)) {
    		lookup_flags |= LOOKUP_REVAL;
    		goto retry;
    	}
    out:
    	revert_creds(old_cred);
    	put_cred(override_cred);
    	return res;
    }
    
    SYSCALL_DEFINE2(access, const char __user *, filename, int, mode)
    {
    	return sys_faccessat(AT_FDCWD, filename, mode);
    }
    
    SYSCALL_DEFINE1(chdir, const char __user *, filename)
    {
    	struct path path;
    	int error;
    	unsigned int lookup_flags = LOOKUP_FOLLOW | LOOKUP_DIRECTORY;
    retry:
    	error = user_path_at(AT_FDCWD, filename, lookup_flags, &path);
    	if (error)
    		goto out;
    
    	error = inode_permission(path.dentry->d_inode, MAY_EXEC | MAY_CHDIR);
    	if (error)
    		goto dput_and_out;
    
    	set_fs_pwd(current->fs, &path);
    
    dput_and_out:
    	path_put(&path);
    	if (retry_estale(error, lookup_flags)) {
    		lookup_flags |= LOOKUP_REVAL;
    		goto retry;
    	}
    out:
    	return error;
    }
    
    SYSCALL_DEFINE1(fchdir, unsigned int, fd)
    {
    	struct fd f = fdget_raw(fd);
    	struct inode *inode;
    	int error = -EBADF;
    
    	error = -EBADF;
    	if (!f.file)
    		goto out;
    
    	inode = file_inode(f.file);
    
    	error = -ENOTDIR;
    	if (!S_ISDIR(inode->i_mode))
    		goto out_putf;
    
    	error = inode_permission(inode, MAY_EXEC | MAY_CHDIR);
    	if (!error)
    		set_fs_pwd(current->fs, &f.file->f_path);
    out_putf:
    	fdput(f);
    out:
    	return error;
    }
    
    SYSCALL_DEFINE1(chroot, const char __user *, filename)
    {
    	struct path path;
    	int error;
    	unsigned int lookup_flags = LOOKUP_FOLLOW | LOOKUP_DIRECTORY;
    retry:
    	error = user_path_at(AT_FDCWD, filename, lookup_flags, &path);
    	if (error)
    		goto out;
    
    	error = inode_permission(path.dentry->d_inode, MAY_EXEC | MAY_CHDIR);
    	if (error)
    		goto dput_and_out;
    
    	error = -EPERM;
    	if (!nsown_capable(CAP_SYS_CHROOT))
    		goto dput_and_out;
    	error = security_path_chroot(&path);
    	if (error)
    		goto dput_and_out;
    
    	set_fs_root(current->fs, &path);
    	error = 0;
    dput_and_out:
    	path_put(&path);
    	if (retry_estale(error, lookup_flags)) {
    		lookup_flags |= LOOKUP_REVAL;
    		goto retry;
    	}
    out:
    	return error;
    }
    
    static int chmod_common(struct path *path, umode_t mode)
    {
    	struct inode *inode = path->dentry->d_inode;
    	struct iattr newattrs;
    	int error;
    
    	error = mnt_want_write(path->mnt);
    	if (error)
    		return error;
    	mutex_lock(&inode->i_mutex);
    	error = security_path_chmod(path, mode);
    	if (error)
    		goto out_unlock;
    	newattrs.ia_mode = (mode & S_IALLUGO) | (inode->i_mode & ~S_IALLUGO);
    	newattrs.ia_valid = ATTR_MODE | ATTR_CTIME;
    	error = notify_change(path->dentry, &newattrs);
    out_unlock:
    	mutex_unlock(&inode->i_mutex);
    	mnt_drop_write(path->mnt);
    	return error;
    }
    
    SYSCALL_DEFINE2(fchmod, unsigned int, fd, umode_t, mode)
    {
    	struct file * file;
    	int err = -EBADF;
    
    	file = fget(fd);
    	if (file) {
    		audit_inode(NULL, file->f_path.dentry, 0);
    		err = chmod_common(&file->f_path, mode);
    		fput(file);
    	}
    	return err;
    }
    
    SYSCALL_DEFINE3(fchmodat, int, dfd, const char __user *, filename, umode_t, mode)
    {
    	struct path path;
    	int error;
    	unsigned int lookup_flags = LOOKUP_FOLLOW;
    retry:
    	error = user_path_at(dfd, filename, lookup_flags, &path);
    	if (!error) {
    		error = chmod_common(&path, mode);
    		path_put(&path);
    		if (retry_estale(error, lookup_flags)) {
    			lookup_flags |= LOOKUP_REVAL;
    			goto retry;
    		}
    	}
    	return error;
    }
    
    SYSCALL_DEFINE2(chmod, const char __user *, filename, umode_t, mode)
    {
    	return sys_fchmodat(AT_FDCWD, filename, mode);
    }
    
    static int chown_common(struct path *path, uid_t user, gid_t group)
    {
    	struct inode *inode = path->dentry->d_inode;
    	int error;
    	struct iattr newattrs;
    	kuid_t uid;
    	kgid_t gid;
    
    	uid = make_kuid(current_user_ns(), user);
    	gid = make_kgid(current_user_ns(), group);
    
    	newattrs.ia_valid =  ATTR_CTIME;
    	if (user != (uid_t) -1) {
    		if (!uid_valid(uid))
    			return -EINVAL;
    		newattrs.ia_valid |= ATTR_UID;
    		newattrs.ia_uid = uid;
    	}
    	if (group != (gid_t) -1) {
    		if (!gid_valid(gid))
    			return -EINVAL;
    		newattrs.ia_valid |= ATTR_GID;
    		newattrs.ia_gid = gid;
    	}
    	if (!S_ISDIR(inode->i_mode))
    		newattrs.ia_valid |=
    			ATTR_KILL_SUID | ATTR_KILL_SGID | ATTR_KILL_PRIV;
    	mutex_lock(&inode->i_mutex);
    	error = security_path_chown(path, uid, gid);
    	if (!error)
    		error = notify_change(path->dentry, &newattrs);
    	mutex_unlock(&inode->i_mutex);
    
    	return error;
    }
    
    SYSCALL_DEFINE5(fchownat, int, dfd, const char __user *, filename, uid_t, user,
    		gid_t, group, int, flag)
    {
    	struct path path;
    	int error = -EINVAL;
    	int lookup_flags;
    
    	if ((flag & ~(AT_SYMLINK_NOFOLLOW | AT_EMPTY_PATH)) != 0)
    		goto out;
    
    	lookup_flags = (flag & AT_SYMLINK_NOFOLLOW) ? 0 : LOOKUP_FOLLOW;
    	if (flag & AT_EMPTY_PATH)
    		lookup_flags |= LOOKUP_EMPTY;
    retry:
    	error = user_path_at(dfd, filename, lookup_flags, &path);
    	if (error)
    		goto out;
    	error = mnt_want_write(path.mnt);
    	if (error)
    		goto out_release;
    	error = chown_common(&path, user, group);
    	mnt_drop_write(path.mnt);
    out_release:
    	path_put(&path);
    	if (retry_estale(error, lookup_flags)) {
    		lookup_flags |= LOOKUP_REVAL;
    		goto retry;
    	}
    out:
    	return error;
    }
    
    SYSCALL_DEFINE3(chown, const char __user *, filename, uid_t, user, gid_t, group)
    {
    	return sys_fchownat(AT_FDCWD, filename, user, group, 0);
    }
    
    SYSCALL_DEFINE3(lchown, const char __user *, filename, uid_t, user, gid_t, group)
    {
    	return sys_fchownat(AT_FDCWD, filename, user, group,
    			    AT_SYMLINK_NOFOLLOW);
    }
    
    SYSCALL_DEFINE3(fchown, unsigned int, fd, uid_t, user, gid_t, group)
    {
    	struct fd f = fdget(fd);
    	int error = -EBADF;
    
    	if (!f.file)
    		goto out;
    
    	error = mnt_want_write_file(f.file);
    	if (error)
    		goto out_fput;
    	audit_inode(NULL, f.file->f_path.dentry, 0);
    	error = chown_common(&f.file->f_path, user, group);
    	mnt_drop_write_file(f.file);
    out_fput:
    	fdput(f);
    out:
    	return error;
    }
    
    /*
     * You have to be very careful that these write
     * counts get cleaned up in error cases and
     * upon __fput().  This should probably never
     * be called outside of __dentry_open().
     */
    static inline int __get_file_write_access(struct inode *inode,
    					  struct vfsmount *mnt)
    {
    	int error;
    	error = get_write_access(inode);
    	if (error)
    		return error;
    	/*
    	 * Do not take mount writer counts on
    	 * special files since no writes to
    	 * the mount itself will occur.
    	 */
    	if (!special_file(inode->i_mode)) {
    		/*
    		 * Balanced in __fput()
    		 */
    		error = __mnt_want_write(mnt);
    		if (error)
    			put_write_access(inode);
    	}
    	return error;
    }
    
    int open_check_o_direct(struct file *f)
    {
    	/* NB: we're sure to have correct a_ops only after f_op->open */
    	if (f->f_flags & O_DIRECT) {
    		if (!f->f_mapping->a_ops ||
    		    ((!f->f_mapping->a_ops->direct_IO) &&
    		    (!f->f_mapping->a_ops->get_xip_mem))) {
    			return -EINVAL;
    		}
    	}
    	return 0;
    }
    
    static int do_dentry_open(struct file *f,
    			  int (*open)(struct inode *, struct file *),
    			  const struct cred *cred)
    {
    	static const struct file_operations empty_fops = {};
    	struct inode *inode;
    	int error;
    
    	f->f_mode = OPEN_FMODE(f->f_flags) | FMODE_LSEEK |
    				FMODE_PREAD | FMODE_PWRITE;
    
    	if (unlikely(f->f_flags & O_PATH))
    		f->f_mode = FMODE_PATH;
    
    	path_get(&f->f_path);
    	inode = f->f_inode = f->f_path.dentry->d_inode;
    	if (f->f_mode & FMODE_WRITE) {
    		error = __get_file_write_access(inode, f->f_path.mnt);
    		if (error)
    			goto cleanup_file;
    		if (!special_file(inode->i_mode))
    			file_take_write(f);
    	}
    
    	f->f_mapping = inode->i_mapping;
    	file_sb_list_add(f, inode->i_sb);
    
    	if (unlikely(f->f_mode & FMODE_PATH)) {
    		f->f_op = &empty_fops;
    		return 0;
    	}
    
    	f->f_op = fops_get(inode->i_fop);
    
    	error = security_file_open(f, cred);
    	if (error)
    		goto cleanup_all;
    
    	error = break_lease(inode, f->f_flags);
    	if (error)
    		goto cleanup_all;
    
    	if (!open && f->f_op)
    		open = f->f_op->open;
    	if (open) {
    		error = open(inode, f);
    		if (error)
    			goto cleanup_all;
    	}
    	if ((f->f_mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
    		i_readcount_inc(inode);
    
    	f->f_flags &= ~(O_CREAT | O_EXCL | O_NOCTTY | O_TRUNC);
    
    	file_ra_state_init(&f->f_ra, f->f_mapping->host->i_mapping);
    
    	return 0;
    
    cleanup_all:
    	fops_put(f->f_op);
    	file_sb_list_del(f);
    	if (f->f_mode & FMODE_WRITE) {
    		put_write_access(inode);
    		if (!special_file(inode->i_mode)) {
    			/*
    			 * We don't consider this a real
    			 * mnt_want/drop_write() pair
    			 * because it all happenend right
    			 * here, so just reset the state.
    			 */
    			file_reset_write(f);
    			__mnt_drop_write(f->f_path.mnt);
    		}
    	}
    cleanup_file:
    	path_put(&f->f_path);
    	f->f_path.mnt = NULL;
    	f->f_path.dentry = NULL;
    	f->f_inode = NULL;
    	return error;
    }
    
    /**
     * finish_open - finish opening a file
     * @od: opaque open data
     * @dentry: pointer to dentry
     * @open: open callback
     *
     * This can be used to finish opening a file passed to i_op->atomic_open().
     *
     * If the open callback is set to NULL, then the standard f_op->open()
     * filesystem callback is substituted.
     */
    int finish_open(struct file *file, struct dentry *dentry,
    		int (*open)(struct inode *, struct file *),
    		int *opened)
    {
    	int error;
    	BUG_ON(*opened & FILE_OPENED); /* once it's opened, it's opened */
    
    	file->f_path.dentry = dentry;
    	error = do_dentry_open(file, open, current_cred());
    	if (!error)
    		*opened |= FILE_OPENED;
    
    	return error;
    }
    EXPORT_SYMBOL(finish_open);
    
    /**
     * finish_no_open - finish ->atomic_open() without opening the file
     *
     * @od: opaque open data
     * @dentry: dentry or NULL (as returned from ->lookup())
     *
     * This can be used to set the result of a successful lookup in ->atomic_open().
     * The filesystem's atomic_open() method shall return NULL after calling this.
     */
    int finish_no_open(struct file *file, struct dentry *dentry)
    {
    	file->f_path.dentry = dentry;
    	return 1;
    }
    EXPORT_SYMBOL(finish_no_open);
    
    struct file *dentry_open(const struct path *path, int flags,
    			 const struct cred *cred)
    {
    	int error;
    	struct file *f;
    
    	validate_creds(cred);
    
    	/* We must always pass in a valid mount pointer. */
    	BUG_ON(!path->mnt);
    
    	f = get_empty_filp();
    	if (!IS_ERR(f)) {
    		f->f_flags = flags;
    		f->f_path = *path;
    		error = do_dentry_open(f, NULL, cred);
    		if (!error) {
    			/* from now on we need fput() to dispose of f */
    			error = open_check_o_direct(f);
    			if (error) {
    				fput(f);
    				f = ERR_PTR(error);
    			}
    		} else { 
    			put_filp(f);
    			f = ERR_PTR(error);
    		}
    	}
    	return f;
    }
    EXPORT_SYMBOL(dentry_open);
    
    static inline int build_open_flags(int flags, umode_t mode, struct open_flags *op)
    {
    	int lookup_flags = 0;
    	int acc_mode;
    
    	if (flags & O_CREAT)
    		op->mode = (mode & S_IALLUGO) | S_IFREG;
    	else
    		op->mode = 0;
    
    	/* Must never be set by userspace */
    	flags &= ~FMODE_NONOTIFY & ~O_CLOEXEC;
    
    	/*
    	 * O_SYNC is implemented as __O_SYNC|O_DSYNC.  As many places only
    	 * check for O_DSYNC if the need any syncing at all we enforce it's
    	 * always set instead of having to deal with possibly weird behaviour
    	 * for malicious applications setting only __O_SYNC.
    	 */
    	if (flags & __O_SYNC)
    		flags |= O_DSYNC;
    
    	/*
    	 * If we have O_PATH in the open flag. Then we
    	 * cannot have anything other than the below set of flags
    	 */
    	if (flags & O_PATH) {
    		flags &= O_DIRECTORY | O_NOFOLLOW | O_PATH;
    		acc_mode = 0;
    	} else {
    		acc_mode = MAY_OPEN | ACC_MODE(flags);
    	}
    
    	op->open_flag = flags;
    
    	/* O_TRUNC implies we need access checks for write permissions */
    	if (flags & O_TRUNC)
    		acc_mode |= MAY_WRITE;
    
    	/* Allow the LSM permission hook to distinguish append
    	   access from general write access. */
    	if (flags & O_APPEND)
    		acc_mode |= MAY_APPEND;
    
    	op->acc_mode = acc_mode;
    
    	op->intent = flags & O_PATH ? 0 : LOOKUP_OPEN;
    
    	if (flags & O_CREAT) {
    		op->intent |= LOOKUP_CREATE;
    		if (flags & O_EXCL)
    			op->intent |= LOOKUP_EXCL;
    	}
    
    	if (flags & O_DIRECTORY)
    		lookup_flags |= LOOKUP_DIRECTORY;
    	if (!(flags & O_NOFOLLOW))
    		lookup_flags |= LOOKUP_FOLLOW;
    	op->lookup_flags = lookup_flags;
    	return 0;
    }
    
    /**
     * file_open_name - open file and return file pointer
     *
     * @name:	struct filename containing path to open
     * @flags:	open flags as per the open(2) second argument
     * @mode:	mode for the new file if O_CREAT is set, else ignored
     *
     * This is the helper to open a file from kernelspace if you really
     * have to.  But in generally you should not do this, so please move
     * along, nothing to see here..
     */
    struct file *file_open_name(struct filename *name, int flags, umode_t mode)
    {
    	struct open_flags op;
    	int err = build_open_flags(flags, mode, &op);
    	return err ? ERR_PTR(err) : do_filp_open(AT_FDCWD, name, &op);
    }
    
    /**
     * filp_open - open file and return file pointer
     *
     * @filename:	path to open
     * @flags:	open flags as per the open(2) second argument
     * @mode:	mode for the new file if O_CREAT is set, else ignored
     *
     * This is the helper to open a file from kernelspace if you really
     * have to.  But in generally you should not do this, so please move
     * along, nothing to see here..
     */
    struct file *filp_open(const char *filename, int flags, umode_t mode)
    {
    	struct filename name = {.name = filename};
    	return file_open_name(&name, flags, mode);
    }
    EXPORT_SYMBOL(filp_open);
    
    struct file *file_open_root(struct dentry *dentry, struct vfsmount *mnt,
    			    const char *filename, int flags)
    {
    	struct open_flags op;
    	int err = build_open_flags(flags, 0, &op);
    	if (err)
    		return ERR_PTR(err);
    	if (flags & O_CREAT)
    		return ERR_PTR(-EINVAL);
    	if (!filename && (flags & O_DIRECTORY))
    		if (!dentry->d_inode->i_op->lookup)
    			return ERR_PTR(-ENOTDIR);
    	return do_file_open_root(dentry, mnt, filename, &op);
    }
    EXPORT_SYMBOL(file_open_root);
    
    long do_sys_open(int dfd, const char __user *filename, int flags, umode_t mode)
    {
    	struct open_flags op;
    	int fd = build_open_flags(flags, mode, &op);
    	struct filename *tmp;
    
    	if (fd)
    		return fd;
    
    	tmp = getname(filename);
    	if (IS_ERR(tmp))
    		return PTR_ERR(tmp);
    
    	fd = get_unused_fd_flags(flags);
    	if (fd >= 0) {
    		struct file *f = do_filp_open(dfd, tmp, &op);
    		if (IS_ERR(f)) {
    			put_unused_fd(fd);
    			fd = PTR_ERR(f);
    		} else {
    			fsnotify_open(f);
    			fd_install(fd, f);
    		}
    	}
    	putname(tmp);
    	return fd;
    }
    
    SYSCALL_DEFINE3(open, const char __user *, filename, int, flags, umode_t, mode)
    {
    	if (force_o_largefile())
    		flags |= O_LARGEFILE;
    
    	return do_sys_open(AT_FDCWD, filename, flags, mode);
    }
    
    SYSCALL_DEFINE4(openat, int, dfd, const char __user *, filename, int, flags,
    		umode_t, mode)
    {
    	if (force_o_largefile())
    		flags |= O_LARGEFILE;
    
    	return do_sys_open(dfd, filename, flags, mode);
    }
    
    #ifndef __alpha__
    
    /*
     * For backward compatibility?  Maybe this should be moved
     * into arch/i386 instead?
     */
    SYSCALL_DEFINE2(creat, const char __user *, pathname, umode_t, mode)
    {
    	return sys_open(pathname, O_CREAT | O_WRONLY | O_TRUNC, mode);
    }
    
    #endif
    
    /*
     * "id" is the POSIX thread ID. We use the
     * files pointer for this..
     */
    int filp_close(struct file *filp, fl_owner_t id)
    {
    	int retval = 0;
    
    	if (!file_count(filp)) {
    		printk(KERN_ERR "VFS: Close: file count is 0\n");
    		return 0;
    	}
    
    	if (filp->f_op && filp->f_op->flush)
    		retval = filp->f_op->flush(filp, id);
    
    	if (likely(!(filp->f_mode & FMODE_PATH))) {
    		dnotify_flush(filp, id);
    		locks_remove_posix(filp, id);
    	}
    	fput(filp);
    	return retval;
    }
    
    EXPORT_SYMBOL(filp_close);
    
    /*
     * Careful here! We test whether the file pointer is NULL before
     * releasing the fd. This ensures that one clone task can't release
     * an fd while another clone is opening it.
     */
    SYSCALL_DEFINE1(close, unsigned int, fd)
    {
    	int retval = __close_fd(current->files, fd);
    
    	/* can't restart close syscall because file table entry was cleared */
    	if (unlikely(retval == -ERESTARTSYS ||
    		     retval == -ERESTARTNOINTR ||
    		     retval == -ERESTARTNOHAND ||
    		     retval == -ERESTART_RESTARTBLOCK))
    		retval = -EINTR;
    
    	return retval;
    }
    EXPORT_SYMBOL(sys_close);
    
    /*
     * This routine simulates a hangup on the tty, to arrange that users
     * are given clean terminals at login time.
     */
    SYSCALL_DEFINE0(vhangup)
    {
    	if (capable(CAP_SYS_TTY_CONFIG)) {
    		tty_vhangup_self();
    		return 0;
    	}
    	return -EPERM;
    }
    
    /*
     * Called when an inode is about to be open.
     * We use this to disallow opening large files on 32bit systems if
     * the caller didn't specify O_LARGEFILE.  On 64bit systems we force
     * on this flag in sys_open.
     */
    int generic_file_open(struct inode * inode, struct file * filp)
    {
    	if (!(filp->f_flags & O_LARGEFILE) && i_size_read(inode) > MAX_NON_LFS)
    		return -EOVERFLOW;
    	return 0;
    }
    
    EXPORT_SYMBOL(generic_file_open);
    
    /*
     * This is used by subsystems that don't want seekable
     * file descriptors. The function is not supposed to ever fail, the only
     * reason it returns an 'int' and not 'void' is so that it can be plugged
     * directly into file_operations structure.
     */
    int nonseekable_open(struct inode *inode, struct file *filp)
    {
    	filp->f_mode &= ~(FMODE_LSEEK | FMODE_PREAD | FMODE_PWRITE);
    	return 0;
    }
    
    EXPORT_SYMBOL(nonseekable_open);